It is known that power is transferred from higher to lower frequencies (from lower to higher wavelengths) and thus between data transmission channels in optical fibers by stimulated Raman scattering (SRS). Thus, the original frequency spectrum of the light signal is “tilted”. This reduces the received power of the channels with short wavelengths; thus, increasing their bit error rate. It is also known to measure the tilting of the spectrum of light signals that are guided through optical fibers, particularly of optical data transmission paths, and to counteract this tilting by appropriate filtering or amplification.
In order to determine this tilting, use is made in the prior art of a complicated spectrally resolving measuring technique that cannot be widely applied because of the expensive and bulky measurement technology.
Furthermore, there is known from U.S. Pat. No. 5,818,629 a method and an arrangement for determining a mean wavelength (“momental wavelength”) of the transmitted light signals, and a control, dependent thereon, of an optical amplifier for compensating for the tilting of the spectrum of the transmitted light signals, in the case of which the “momental wavelength” of the injected light signals is determined in a “monitoring device” (see FIG. 1). The mean wavelength (“momental wavelength”) is used to determine the tilting of the spectrum of the injected light signals within the optical transmission system, and to control the amplification of the optical amplifier so as to virtually compensate for the determined tilting of the spectrum. Such a method requires the technically complicated determination of the mean wavelength and the evaluation thereof.
It is, therefore, an object of the present invention to develop a method that can determine the tilting of the spectrum in an optical fiber in a simple and quick way without a spectrally resolving measuring technique.